1. Field of the Invention
The present invention relates generally to apparatuses and methods for transporting and metering particulate material and, in particular embodiments, to an improved particulate material handling device which can be used to both transport and meter solid material of a great range of sizes under both ambient conditions and against pressure.
2. Description of Related Art
A wide variety of equipment has been used to either transport or meter particulate material (such as, but not limited to, coal, other mined materials, dry food products, other dry goods handled in solid, particle form). Such transport equipment includes conveyor belts, rotary valves, lock hoppers, screw-type feeders, etc. Exemplary measurement or metering devices include weigh belts, volumetric hoppers and the like. In order to provide both transport and metering of particulate material, it was typically necessary to use or combine both types of devices into a system.
However, some of applicant's prior pump devices were provided with the capability of both transporting and metering particulate material. Examples of such prior designs include the rotary disk type pumps discussed in the following U.S. patents, each of which is assigned or licensed to the assignee of present invention and each of which is incorporated herein by reference: U.S. Pat. No. 4,516,674 (issued May 14, 1985); U.S. Pat. No. 4,988,239 (issued Jan. 29, 1991); and U.S. Pat. No. 5,051,041 (issued Sep. 24, 1991). While some of these prior pump designs have shown some capacity to pump particulate material against a relatively low pressure head, such pumps have not been capable of pumping against a significantly larger gas or fluid pressure head.
There are many instances in which it is desirable to transport and meter particulate materials against pressure (e.g., wherein gas and/or fluid pressure at the output side of the transport system is greater than the gas and/or fluid pressure at the input side of the system). It would be desirable to provide an apparatus which is capable of pumping and metering under both ambient pressure conditions and against a pressure head caused either by entry into a pressurized environment (wherein the gas and/or fluid pressure of the environment on the output side of the apparatus is greater than such at the input side).
A number of factors must be considered in the design of an efficient device for transporting or metering particulate materials. For example, the amount, size and type of particulate material to be transported must be taken into consideration. The distance over which the material is to be transported and variations in the surrounding pressure during transport must also be taken into account. It would be desirable to provide a pump device which is capable of transporting and metering a wide variety of particulate materials under both ambient and pressurized conditions.
Large scale transport and/or metering of particulate material presents unique problems. A transport apparatus or system which is suitable for transporting one type of particulate material may not be suitable for transporting a different type of material. For example, Kentucky coals maintain reasonable integrity when transported through conventional devices such as screw feeders and conveyor belts. However, Western United States coals tend to be more friable and may be degraded to a significant degree during normal transfer operations. It would be desirable to provide an apparatus which is capable of transferring all types of coal (or other friable materials) with a minimum amount of degradation under both ambient and pressurized conditions.
The water content of the particulate solids is another factor which must be considered when designing any transport system. Many transport devices which are suitable for transporting completely dry particles do not function properly when the moisture content of the particulate material is raised. The same is true for particulate metering devices. Conventional metering devices which are designed to measure dry particulates may not be well suited to meter moist solids. It would be desirable to provide a transport apparatus which is capable of moving and/or metering particulate solids regardless of their moisture content under both ambient and pressurized conditions.
It is apparent from the above background that there is a present need for a solids handling or pumping device which operates as a single unit to provide simultaneous transport and metering of particulate material in ambient and pressurized conditions. The unit should be capable of transporting and metering a wide variety of particle types under a wide variety of conditions. Further, the unit should be structurally strong, and mechanically simple and durable so that it can be operated continuously over extended periods of time without failure.